[esnext] implement frontend changes for async/await proposal

src/parsing/expression-classifier.h

Index: src/parsing/expression-classifier.h
diff --git a/src/parsing/expression-classifier.h b/src/parsing/expression-classifier.h
index dfb582d326504bee5aa4d246432d1749f104a2d2..cb24011a5655451a684ca4d2a60e0376346b20e4 100644
--- a/src/parsing/expression-classifier.h
+++ b/src/parsing/expression-classifier.h
@@ -40,6 +40,7 @@ class ExpressionClassifier {
     LetPatternProduction = 1 << 7,
     CoverInitializedNameProduction = 1 << 8,
     TailCallExpressionProduction = 1 << 9,
+    AsyncArrowFormalParametersProduction = 1 << 10,
 
     ExpressionProductions =
         (ExpressionProduction | FormalParameterInitializerProduction |
@@ -51,7 +52,8 @@ class ExpressionClassifier {
     StandardProductions = ExpressionProductions | PatternProductions,
     AllProductions =
         (StandardProductions | FormalParametersProductions |
-         ArrowFormalParametersProduction | CoverInitializedNameProduction)
+         ArrowFormalParametersProduction | CoverInitializedNameProduction |
+         AsyncArrowFormalParametersProduction)
   };
 
   enum FunctionProperties { NonSimpleParameter = 1 << 0 };
@@ -112,6 +114,10 @@ class ExpressionClassifier {
 
   bool is_valid_let_pattern() const { return is_valid(LetPatternProduction); }
 
+  bool is_valid_async_arrow_formal_parameters() const {
+    return is_valid(AsyncArrowFormalParametersProduction);
+  }
+
   const Error& expression_error() const { return expression_error_; }
 
   const Error& formal_parameter_initializer_error() const {
@@ -151,6 +157,9 @@ class ExpressionClassifier {
   const Error& tail_call_expression_error() const {
     return tail_call_expression_error_;
   }
+  const Error& async_arrow_formal_parameters_error() const {
+    return async_arrow_formal_parameters_error_;
+  }
 
   bool is_simple_parameter_list() const {
     return !(function_properties_ & NonSimpleParameter);
@@ -228,6 +237,16 @@ class ExpressionClassifier {
     arrow_formal_parameters_error_.arg = arg;
   }
 
+  void RecordAsyncArrowFormalParametersError(const Scanner::Location& loc,
+                                             MessageTemplate::Template message,
+                                             const char* arg = nullptr) {
+    if (!is_valid_async_arrow_formal_parameters()) return;
+    invalid_productions_ |= AsyncArrowFormalParametersProduction;
+    async_arrow_formal_parameters_error_.location = loc;
+    async_arrow_formal_parameters_error_.message = message;
+    async_arrow_formal_parameters_error_.arg = arg;
+  }
+
   void RecordDuplicateFormalParameterError(const Scanner::Location& loc) {
     if (!is_valid_formal_parameter_list_without_duplicates()) return;
     invalid_productions_ |= DistinctFormalParametersProduction;
@@ -326,6 +345,9 @@ class ExpressionClassifier {
         cover_initialized_name_error_ = inner->cover_initialized_name_error_;
       if (errors & TailCallExpressionProduction)
         tail_call_expression_error_ = inner->tail_call_expression_error_;
+      if (errors & AsyncArrowFormalParametersProduction)
+        async_arrow_formal_parameters_error_ =
+            inner->async_arrow_formal_parameters_error_;
     }
 
     // As an exception to the above, the result continues to be a valid arrow
@@ -373,6 +395,7 @@ class ExpressionClassifier {
   Error let_pattern_error_;
   Error cover_initialized_name_error_;
   Error tail_call_expression_error_;
+  Error async_arrow_formal_parameters_error_;
   DuplicateFinder* duplicate_finder_;
 };